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Flashcards in 1. Intro (I) Deck (55):
1

Bacteria that are not stained through Gram Staining

Chlamydia
Legionella
Mycoplasma

2

Gram stain procedure

Crystal violet (1° stain)
Gram's iodine (Mordant)
Acetone / alcohol (Decolorizer)
Safranin (Counterstain)

COAM

3

What is the difference between Gram+ and Gram- cell walls?

Cell walls of gram-negative cells have higher lipid content that gram-positive cells

4

Special consideration of Gram Stain of sputum specimen; if >25 epithelial cells/lpf

Saliva

5

Special consideration of Gram Stain of sputum specimen; few epithelial cells, many PMN cells

Specimen more likely to yield a pathogen

6

When can you say that a sputum specimen is actually saliva?

When there are >25 epithelial cells/lpf

7

When can you say that a sputum specimen may likely yield a pathogen?

When there are few epithelial cells and many PMN cells

8

Special consideration for urine specimen

1 cell per oil immersion field = approx. 1x10^5 CFU/mL

9

Enumerate the quantitation criteria for Gram Stain

- no organisms seen
- Few per slide = rare
- 0 to 2 per field = few
- 2 to 10 per field = moderate
- more than 10 per field = many

10

Constituents of media

Agar
Nutrients
Enrichments
Buffers
pH indicators
Inhibitors

BEANpI

11

Constituent of media; gelatinous seaweed extract

Agar

12

Percent of agar in plates

1-2% agar in plates

13

Nutrients in media can be _______ or _______

Hydrolyzed proteins (animal or plant)
Carbohydrates/sugars

14

Enrichments used in media

Yeast extracts
Blood

15

Purpose of buffers in media

Provides a stable pH for growth

16

pH indicators used in media and their colors

Neutral red: red to colorless
Phenol red: yellow to red
Thymol blue: yellow to green/blue

17

Inhibitors in media

Bile salts
Antibiotics
Dyes
Sodium chloride
Sodium citrate

BADSS

18

Examples of dyes used as inhibitors in media

Crystal violet
Eosin
Methylene blue

19

Example of bile salt used as inhibitor in media

Sodium deoxycholate

20

Agar that contains inhibitory agents to all organisms except one being sought

Selective agar

21

Example of selective agars

Colistine nalidixic acid agar (CNA)
MacConkey Agar

22

Agar that selects for certain organisms to the disadvantage of others

Selective agar

23

Agar that allows organism to be morphologically distinguished from other organisms with different characteristics

Differential agar

24

Examples of differential agar

Sheep blood agar (SBA)
MacConkey agar

25

Supportive media aerobic cultures

Blood agar
Chocolate agar

26

Selective/differential media for gram-negative aerobic bacilli

MacConkey agar
Xylose Lysine Desoxycholate (XLD) agar
Hektoen Enteric Agar (HEA)

27

Selective/differential media for gram-positive aerobic organisms

Colistin Nalidixic Acid (CNA) agar
Phenylethyl Alcohol Agar (PEA)

28

Purpose of Blood Agar for aerobes

General growth of gram-positive and gram-negative aerobes

29

Why is the Blood Agar also considered as differential aside from being supportive?

Because organisms may demonstrate hemolytic patterns

30

Chocolate agar is used for

Isolation of fastidious organisms:
- Haemophilus spp.
- Neisseria spp.
- Brucella spp.
- Capnocytophaga spp.

31

Components of MacConkey agar

Lactose
Crystal violet
Bile salts

32

pH indicator in MacConkey agar

Neutral red

33

Purpose of lactose in MacConkey agar

- Provides fermentable sugar (Lactose positive vs negative)
- Lactose fermenting vs non-lactose fermenting organism

34

Purpose of crystal violet in MacConkey agar

Inhibits gram-positive bacteria

35

Purpose of bile salts in MacConkey agar

Inhibits gram-positive bacteria

36

MacConkey agar is selective for

Gram-negative organisms

37

Lactose positive bacteria (lactose fermenters)

Escherichia coli: dry, flat, dark pigment
Enterobacter: mucoid
Citrobacter: late fermenter
Klebsiella: mucoid
Serratia: late, red pigment (some)

EECKS

38

Lactose negative bacteria (non-lactose fermenters)

Proteus: swarming
Providencia
Pseudomonas
Hafnia
Edwardsiella
Morganella
Salmonella
Shigella

P3HEMS2

39

Component of XLD; inhibits gram-positive organisms

Sodium deoxycholate

40

pH indicator of XLD

Phenol red

41

Carbohydrate components in XLD

Lactose
Sucrose
Xylose

42

Carbohydrates in XLD that provide fermentable sugar

Lactose
Sucrose

43

Enzyme detected by lysine in XLD agar

Lysine decarboxylase

44

Effect of Salmonella to lysine in XLD agar

Since Salmonella has lysine decarboxylase, the lysine in the agar is decarboxylated, shifting the pH indicator to red

45

Component of XLD; detects production of H2S

Sodium thiosulfate
Ferric ammonium citrate

46

Characteristics of E. coli in XLD

Yellow color; ferments carbohydrates; causes large pH drop

47

Characteristics of Shigella and Providencia in XLD

Colorless or red; no fermentation; no H2S

48

Characteristics of Salmonella in XLD

Red with black center; ferments xylose; produces low pH; then decarboxylates lysine; produces high pH; H2S production

49

Purpose of sodium deoxycholate in XLD

Inhibits gram-positive organisms

50

Organism(s) that ferments carbohydrates in XLD, causes large pH drop, yellow color

E. coli

51

Organism(s) that is/are colorless or red in XLD; no fermentation, no H2S production

Shigella
Providencia

52

Organism that produce red color with black center in XLD, ferments xylose, produces low pH, then decarboxylates lysine, produces high pH, H2S production

Salmonella

53

What is the X factor in the chocolate agar?

Hemin

IsoVitaleX Enrichment (according to Elsevier reviewer)

54

What is the V factor in the chocolate agar?

Nicotinamide adenine dinucleotide (NAD)

Hemoglobin (according to Elsevier reviewer)

55

Developer of Gram Stain

Hans Christian Gram (1884)